Rotary electric machines have been required to reduce the lengths (heights) between both stator coil ends of a stator from an annular cylindrical stator core thereof while increasing the winding packing factor of the stator. In order to meet the requirement, rotary electric machines, each of which installs therein an annular-shaped stator with a sequentially joined-segment stator coil, have been proposed.
The sequentially joined-segment stator coil includes a plurality of conductor segments, and each of the conductor segments consists of a pair of straight portions and a U-shaped turn portion joining the paired straight portions. A plurality of slots are circumferentially arranged in the stator core with given intervals.
One of the paired straight portions of one of the conductor segments is installed in one slot of a stator core and the other thereof is installed in another one slot thereof; these one slot and another slot are formed through the stator core to be circumferentially arranged with an interval corresponding to a substantially pole pitch of a rotor. One end of each of the straight portions of one of the conductor segments projecting from a corresponding slot is inclined in a circumferential direction of the stator core. Similarly, the remaining conductor segments are installed in corresponding pairs of slots of the stator core, respectively.
Joining the projecting end of each of the straight portions of each conductor segment installed in the stator core to the projecting end of a corresponding one of the straight portions of a corresponding one of the conductor segments installed in the stator core forms a continuous stator winding.
One example of methods of joining such conductor segments is disclosed in U.S. Pat. No. 6,698,083 B2 corresponding to Japanese Patent Application Publication No. 2000-350422.
In the U.S. Pat. No. 6,698,083, four straight portions of one and another one conductor segments are installed in a same slot of an annular cylindrical stator core in a radial direction thereof. The projecting end of each of the straight portions of each conductor segment installed in a slot of the stator core is sequentially joined to that of a corresponding one of the straight portions of a corresponding one of the conductor segments installed in another slot of the stator core. This results that at least one continuous stator winding of a stator coil is formed.
Specifically, as illustrated in FIG. 9, one projecting end of one large conductor segment 200a, one projecting end of one small conductor segment 200b to be joined thereto, one projecting end of another one large conductor segment 200a, and one projecting end of another one small conductor segment 200b are aligned in a radial direction of a stator core 210.
Note that the innermost projecting end of one large conductor segment 200a, the inner middle projecting end of one small conductor segment 200b, the outer middle projecting end of another one small conductor segment 200a, and the outermost projecting end of another one large conductor segment 200b are respectively referred to as “first projecting end 201”, “second projecting end 202”, “third projecting end 203”, and “fourth projecting end 204”. The first and second projecting ends 201 and 202 constitute an inner end pair 211, and the third and fourth projecting ends 203 and 204 constitute an outer end pair 212.
The first projecting end 201 is pressed toward a radially outer side by an inner ground electrode 205 located at the inner side of the stator core 210; this results that the first projecting end 201 and the second projecting end 202 are contacted to be electrically conducted therebetween to constitute the inner end pair 211. In this electrical conducting state, a welding torch 220 as a welding electrode of a welding system is arranged close to the inner end pair 211, and thereafter, arc discharge is carried out between the inner ground electrode 205 and the welding torch 220. This allows the first projecting end 201 and the second projecting end 202 to be respectively melted, and therefore, they are joined to each other.
Similarly, the fourth projecting end 204 is pressed toward a radially inner side by an outer ground electrode 206 located at the outer side of the stator core 210; this results that the fourth projecting end 204 and the third projecting end 203 are contacted to be electrically conducted therebetween to constitute the outer end pair 212. In this electrical conducting state, the welding torch 220 is arranged close to the outer end pair 212, and thereafter, arc discharge is carried out between the outer ground electrode 206 and the welding torch 220. This allows the fourth projecting end 204 and the third projecting end 203 to be respectively melted, and therefore, they are joined to each other.
Each of the conductor segments 200 is normally coated with an insulating film. In order to generate the arc discharge between the arc torch 220 and each of the inner and outer ground electrodes 205 and 206, electrical conduction between each of the conductor segments 200 and a corresponding one of the inner and outer ground electrodes 205 and 206 is needed. The insulating film located at one side of each of the first to fourth projecting ends 201 to 204 of the conductor segments 200 is eliminated before or after the insertion of each conductor segment 200 into a corresponding pair of slots of the stator core 210 with a cutter or chemical.
For example, the insulating film located at one side of each of the first to fourth projecting ends 201 to 204 of the conductor segments 200 is eliminated by cutting it or removing it by a chemical agent. Thereafter, the inner ground electrode 205 or the outer ground electrode 206 is directly contacted onto one side of each of the first to fourth projecting ends 201 to 204 of the conductor segments 200 so as to be directly conducted thereto; this allows an are to be discharged therebetween.
This conductor-segment joining method disclosed in U.S. Pat. No. 6,698,083 is designed to alternators whose stator coils are each configured such that:
four straight portions of different conductor segments are installed in each of the slots of the stator core; and
an inner end pair of projecting ends of respective straight portions of different conductor segments and an outer end pair of projecting ends of respective straight portions of different conductor segments are aligned in a radial direction of the stator core over each slot of the stator core. Note that such a configuration of a stator coil having four straight portions of different conductor segments installed in each slot and having the inner and outer coil end pairs will be referred to as “four-layer and two-row configuration” hereinafter.
Let us consider that the conductor-segment joining method disclosed in U.S. Pat. No. 6,698,083 is applied to high power output motors, such as motors for automobiles. In this application, the stator coil of the high power output motors are comprised of:
a great number of straight portions of different conductor segments are installed in each of the slots of the stator core; and
a great number of pairs of projecting ends of respective straight portions of different conductor segments are aligned in a radial direction of the stator core over each slot of the stator core. Note that such a configuration of a stator coil having a great-number of straight portions of different conductor segments installed in each slot and having a great number of pairs of projecting ends will be referred to as “many-layer and many-row configuration” hereinafter.
The many-layer and many-row configuration of the stator coil can increase the number of turns of the stator coil in each phase.
In the many-layer and many-row configuration of the stator coil, a plurality of projecting ends are disposed between the inner end pair and the outer end pair. The conductor-segment joining method disclosed in U.S. Pat. No. 6,698,083 allows electrical conduction of the inner end pair and that of the outer end pair because of arrangement of each of the inner ground electrode 205 and the outer ground electrode 206. However, it may be difficult to establish electrical conduction of the plurality of projecting ends disposed between the inner end pair and the outer end pair using the inner and outer ground electrodes 205 and 206. Note that such plurality of projecting ends disposed between the inner end pair and the outer end pair will be referred to as intermediate projecting ends hereinafter.
Thus, in the many-layer and many-row configuration of the stator coil, how to establish electrical conduction between the middle projecting ends continues to be an important issue.
In order to address the important issue, first and second methods are proposed.
The first method includes the steps of:
arranging a pair of new intermediate ground electrodes at both circumferential sides of each pair of radially adjacent intermediate ground projecting ends;
causing the paired new electrodes to circumferentially clip the radially adjacent intermediate projecting ends of each pair so as to contact them; and
discharging, with the use of a welding torch of an arc welding system, an arc between the paired new electrodes via the clipped radially adjacent intermediate projecting ends of each pair.
The second method includes the steps of:
arranging radially adjacent pairs of the intermediate projecting ends such that each of the radially adjacent pairs of the intermediate projecting ends is not radially aligned with another one of the radially adjacent pairs thereof and with each of the inner end pair and the outer end pair;
radially moving at least one of the inner and outer ground electrodes so as to make it contact to at least one of the radially adjacent intermediate projecting ends of each pair; and
discharging, with the use of a welding torch, an arc between the at least one of the inner and outer ground electrodes and the welding torch.
In place of the radial moving step, the second method can include the following step:
radially extending at least one of the inner and outer ground electrodes so as to take it contact to at least one of the radially adjacent intermediate projecting ends of each pair.
The first method can keep the radial alignment of the plurality of projecting ends of respective straight portions installed in each slot of the stator core, making it possible to easily install the plurality of stator windings in the stator core.
The second method can easily carry out using such an arc welding without the need for another new intermediate electrode.